Cell Signaling Lecture Flashcards

Vocabulary flashcards covering fundamental terms and concepts of cell signaling, receptor binding properties, messenger classes, and intracellular cascade mechanisms.

Neurotransmitters

A category of chemical messengers released by nerve cells that travel across close proximity to target neurons or effector cells.

Hormones

Chemical messengers secreted by gland cells into blood vessels, targeting cells in one or more distant places in the body.

Paracrine Agents

Chemical messengers released by local cells that target cells in close proximity to the site of release.

Autocrine Agents

Chemical messengers released by local cells that act directly on the same cell that secreted them.

Receptor

A specialized area of the cell membrane sensitive to chemicals that, when activated, causes the cell to change its behavior.

Specificity

A feature of ligand-receptor binding where the binding site of a receptor has a specific shape that fits only specific messengers.

Affinity

The force of binding between a chemical messenger and its receptor.

Saturation

The degree to which the receptors on a cell are fully occupied by a messenger.

Competition

The process in which different molecules with similar chemical structure compete for the same receptor binding site.

Agonist

A chemical messenger that binds to a receptor and triggers the normal response, often mimicking the action of the normal messenger.

Antagonist

A molecule that binds to a receptor but does not elicit a response, often referred to as a blocker.

Down-regulation

A decrease in the total number of receptors for a messenger in response to prolonged high extracellular concentrations, decreasing cell sensitivity.

Up-regulation

An increase in the total number of receptors for a messenger in response to prolonged low extracellular concentrations, increasing cell sensitivity.

Kinases

Intracellular enzymes that add phosphate groups to either intermediate molecules of a cascade or final effector molecules.

Phosphatases

Intracellular enzymes that remove phosphate groups from molecules in a signaling cascade.

Lipid-Soluble Primary Messengers

Lipid-permeable (genomic) messengers that pass through the plasma membrane, bind to intracellular receptors in the cytosol or nucleus, and alter gene transcription and protein synthesis.

Water-Soluble Primary Messengers

Hydrophilic messengers that cannot pass through lipid bilayers and instead bind to plasma membrane receptors to initiate a second messenger cascade.

Janus Kinases (JAK)

Cytoplasmic enzymes that associate with activated cell-surface receptors and phosphorylate intracellular proteins to induce responses like cytokine activity or protein synthesis.

G-Protein Coupled Receptors (GPCR)

The largest family of cell-surface receptors, linked via heterotrimeric G proteins to effector membrane proteins such as ion channels or enzymes.

G Protein Subunits

The three components ($\alpha$, $\beta$, and $\gamma$) of a heterotrimeric G protein; the $\alpha$ subunit binds and hydrolyzes GTP to activate effectors, while $\beta$ and $\gamma$ anchor the complex in the membrane.

Adenylyl Cyclase

A plasma membrane effector enzyme activated by a G protein ($\text{G}_s$) that catalyzes the conversion of ATP into cyclic AMP (cAMP).

Cyclic AMP (cAMP)

An intracellular second messenger produced from ATP by adenylyl cyclase that activates cAMP-dependent protein kinase (Protein Kinase A / PKA).

Phosphodiesterase

An enzyme that breaks down cyclic AMP (cAMP) into linear AMP, effectively terminating the cAMP signaling cascade.

Signal Amplification

A process in signaling cascades where a single primary messenger binding event leads to the generation of a disproportionately large intracellular output (e.g., $1$ epinephrine molecule producing $10^8$ glucose molecules).